Due to the global warming problem every organization has to improve power efficiency. Therefore, energy saving or power optimization is one of the key self-organized networks (SON) use cases in 3rd generation partnership project (3GPP) and next generation mobile networks (NGMN). The use case is about changing network parameters during operational state so that energy consumption of network elements would be minimized and therefore operating or operational expenditure (OPEX) saving (through lower electricity bill) and environmental benefits (less CO2 emission due to lower energy consumption) would be achieved.
In case of a (femto) home node B (HNB), the energy saving or power optimization can solve another more significant problem that becomes more acute when the number of HNBs increases in a given residential area. The problem is that the downlink (DL) transmission of a femto base station generates interference to other neighboring femto cell users and the non-femto users that are connected to an overlay macro cell base station. Minimizing interference caused by femto nodes is essential even just for the normal operation of the networks.
The deployment of HNBs and home enhanced node Bs (HeNBs) is usually performed in an uncoordinated manner, which can lead to a decreased macro and femto network capacity due to increased inter-cell interference. In addition, active H(e)NBs consume energy and generate interference even if there is no traffic, as there may be long periods during which all allowed user equipments (UEs) are outside the cell coverage (working hours, school hours, holidays, outdoor activities, etc.). Thus, it would be advantageous to activate/deactivate H(e)NBs, depending on authorized UEs' locations, in order to reduce energy consumption and interference.
One way to achieve energy saving and interference reduction is to shut down an entire femto cell, which may provide the most gain and the most straightforward approach. For example, a person operating a H(e)NB can switch off the same or disconnect the power line cable thereof when leaving his/her residence or office where the H(e)NB is located. Another way is to switch on or off a H(e)NB when an authorized UE arrives at or leaves the vicinity of the access point formed by the H(e)NB. Such approach is described e.g. in R3-081174, “Solution for interference reduction SON use case”, Orange, Alcatel-Lucent, RAN3#61bis ([R3-081174]) and R3-081123, “Dynamic Setup of HNBs for Energy Savings and Interference Reduction”, Mitsubishi Electric, RAN3#60 ([R3-081123]).
With the previously proposed approaches as described above, the H(e)NB still generates interference and consumes electricity even if no active sessions are created, e.g. during night time when an authorized UE is located in the H(e)NB area but does not make any calls. The previously proposed approaches do not solve the more important interference problem directly. If they provide some solution to this problem at all, it is not effective.